Innervation of the inguinal region arises from the distal extensions of the more cephalad lumbar plexus nerves (i.e., the iliohypogastric and ilioinguinal nerves), which have their origin from the first lumbar nerve, and the genitofemoral nerve, which has its origin from the first and second lumbar nerves (
Fig. 36-1
). These peripheral extensions of the lumbar plexus and the 12th thoracic nerve follow a circular course that is influenced by the bowl-like shape of the ilium. As these nerves course anteriorly (
Fig. 36-2
), they pass near an important landmark for the block, the anterosuperior iliac spine. In the vicinity of the anterosuperior iliac spine, the 12th thoracic and iliohypogastric nerves lie between the internal and external oblique muscles. The ilioinguinal nerve lies between the transversus abdominis muscle and the internal oblique muscle initially and then penetrates the internal oblique muscle some distance medial to the anterosuperior spine. All these nerves continue anterior medially and become superficial as they terminate in the skin and muscles of the inguinal region (
Fig. 36-3
). As is also shown in
Figure 36-3
, the genitofemoral nerve follows a different course, and it is this nerve that must often be supplemented intraoperatively to make this regional block effective for inguinal herniorrhaphy.

Figure 36-1 Inguinal block: anatomy.

Figure 36-2 Inguinal block: anatomy.

Figure 36-3 Inguinal block: anatomy and technique.

Position.

The inguinal block can be carried out with the patient in the supine position and the anesthesiologist at the patient’s side in a position to utilize the anterosuperior iliac spine as a landmark.

Needle Puncture.

While the patient is in the supine position, the anterosuperior iliac spine should be marked. Another mark should be made approximately 3 cm medial and inferior to the anterosuperior iliac spine. A skin wheal is created, and an 8-cm, 22-gauge needle is inserted in a cephalolateral direction (needle position 1) to contact the inner surface of the ilium, as illustrated in
Figure 36-4
. Local anesthetic solution (10 mL) is injected as the needle is slowly withdrawn through the layers of the abdominal wall. The needle is then reinserted at a steeper angle to ensure penetration of all three abdominal muscle layers (needle position 2). Again, the injection is repeated as the needle is withdrawn. A third injection may be necessary at an even steeper angle in patients who are heavily muscled or obese. The injection is extended from the previously placed skin wheal toward the umbilicus, creating a subcutaneous field block. This process is repeated from umbilicus to pubis (
Fig. 36-5
). Again, the possibility that the surgeon will have to inject additional local anesthetic into the cord should be kept in mind, so this necessary part of the block can be added intraoperatively without concern over local anesthetic systemic toxicity.

Figure 36-4 Inguinal block: cross-sectional anatomy and technique.

Figure 36-5 Inguinal block: infiltration technique.

Potential Problems.

The inguinal block is primarily a superficial block and is associated with few major complications. Some proponents of this technique advocate making an injection preoperatively in the region of the inguinal canal and spermatic cord. A potential problem with this additional injection is that hematoma formation is possible in the region of the cord. Although this does not harm the patient, the surgeon may find it difficult to perform an adequate surgical dissection.